The invention relates to a method of manufacturing urea as a nitrogen-rich synthetic fertilizer from refuse of any composition, preferably from domestic waste. The organic waste components are first turned into gas in a high-temperature reactor with oxygen (O2) which has been obtained in a cryogenic air separation plant. A synthesis gas arises which predominantly comprises carbon monoxide (CO), hydrogen (H2) and carbon dioxide (CO2). The carbon monoxide (CO) contained in the synthesis gas is subsequently converted with steam into hydrogen (H2) and carbon dioxide (CO2). The hydrogen is subsequently separated and is used for ammonia synthesis together with the elementary nitrogen (N2) which arises as a by-product in cryogenic air separation. In the last process step, urea (CO(NH2)2) is manufactured from ammonia (NH3) and the further synthesis gas component carbon dioxide (CO2).
The population of the world increased from 3 billion in 1960 to more than 7 billion in 2011. A disproportionately high growth of the world's population must also be anticipated in the next few decades, with the predominant portion of population growth currently taking place in the developing countries or in the less developed and poorer states of the world.
Since the area for agricultural use is limited and since additional usable areas can only be created in a small amount, the feeding of the world's population represents an ever increasing problem. Only if it becomes possible significantly to increase the specific yields of the available usable areas will there be a real chance also to feed the world's population in the future. It is possible to increase the specific yields of the available usable areas by an increased use of fertilizers.
Urea with a nitrogen content of 46.62% is the most important nitrogen fertilizer in the world. Urea is obtained on a large technical scale from natural gas. For this purpose, large chemical plant is used which produces urea from natural gas, air and water in the process steps hydrogen manufacture, ammonia manufacturer and urea synthesis.
Approximately 130 million metric tonnes (t) of urea were produced worldwide in 2009. The price of urea has risen by around 80% to 350 per tonne over the last three years. The increasing natural gas prices and the rising demand for urea will have the result that the urea prices will also rise disproportionately in the future.
To be able to satisfy the increasing demand for urea as a synthetic fertilizer containing nitrogen, means and ways will have to be found to significantly increase annual urea production.
The amount of waste has also risen disproportionately with the population growth and increasing wealth and the search for a more environmentally acceptable solution of the waste problem is becoming more and more important.
An attempt is being made to solve the waste problem in a sustainable manner using thermal waste utilization technologies. The “thermoselect process” is taking up a preeminent position among these thermal processes. In the “thermoselect process”, waste of the most varied composition and consistence is gasified with pure oxygen in a high-temperature reactor at a temperature of up to 2000° C. In this process, a synthesis gas arises which primarily comprises the molecules hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2).
The oxygen used for gasifying the organic waste components is obtained by a cryogenic air separation process corresponding to the prior art. Elementary nitrogen arises as a by-product in this process which has previously been discharged to the atmosphere. The “thermoselect process” is described in EP 0790291 B1 and EP 0726307 B1.